102 SILVEK-LEAD DEPOSITS OF EUREKA, NEVADA. 



present exists in the large ore chambers. In the unchanged ore bodies, 

 which are encountered occasionally near the water, there is nowhere any 

 evidence of the banded structure characteristic of the simple crystallization 

 of minerals from solution. The galena, blende, and pyrite of which these 

 ore masses are principally composed are distributed in bunches and compact 

 masses, and nowhere is there any evidence of paragenetic order. It is true 

 that a paragenesis of minerals is traceable in many places in the oxidized 

 ore, but this is due to successive stages of decomposition. 



Description of the Raiw deposits. — Attention has been already called (Chapter 

 VI.) to Raibl, in Carinthia, where galena and zinc deposits occur in a 

 limestone formation. PoSepny," who very fully describes these deposits, 

 mentions the following facts: The galena deposits occur principally in the 

 dolomite, and the zinc deposits in the underlying limestone. They are to 

 be classed neither as beds nor as lodes. As to the genesis of the ore, they 

 differ very widely; the galena deposits were made in pre-existing cavities 

 in the dolomite, while the zinc ore is pseudomorphous after limestone, or, in 

 other words, was brought into its present position by substitution for coun- 

 try rock. The proofs this author gives of the manner of formation of the 

 lead deposits are very conclusive. The ore, which consists principally of 

 galena, blende, pyrite, and dolomite (cerussite, smithsonite, calcite, and 

 barite being comparatively uncommon), is deposited in concentric layers, 

 the cavities being sometimes completely filled, though often an empty space 

 is found at the center, and hardly admit of a doubt in regard to their being 

 formed by crystallization from solutions. The occurrence of a peculiar 

 tubular galena ore (Rohrenerz), which was formed around pre-existing 

 stalactites of dolomite, effectually establishes the fact that the cavities existed 

 before the ore-bearing solutions made their appearance. As regards the 

 manner of their formation, the zinc deposits are widely different from those 

 of lead. The ores composing them are zinc bloom, smithsonite, calamine, 

 and mixtures of these minerals with manganese and iron oxides, different 

 kinds of iron ores, and peculiar clays. The calamine is seldom found 



a F. PoSepny. Die Blei- nnd Galmei-Erzlagerstiitten von Raibl in Karuten. Jahrb. der k. k. 

 geologischen, Reichsanstalt. Wien, 1873, B. xsiii. 



